Conventionally, technologies for controlling the temperature adjustment of heated bodies such as a reflow furnace and a thermostatic bath are known. While a heated body has a different heat capacity according to its kind, the heated body is frequently heated using one heater having a large power rating as a heating body. This is because it is difficult in view of cost to introduce heaters of various power ratings in accordance with heated bodies having different heat capacities. In addition, it is preferable to control the heating of a heated body such that overshoot or hunting does not occur, and such technologies are disclosed in Patent Literatures 1 and 2.
More specifically, Patent Literature 1 discloses a temperature control device executing auto tuning (AT) of a limit cycle method for setting a PID parameter by generating a limit cycle for outputting an operation amount with a constant amplitude to a power conditioner supplying power to a heater. This temperature control device executes AT of a limit cycle method for each of upper limit values of a plurality of operation amounts registered in advance and stores the amplitude of temperature that is a control target at the time of executing AT for each of the upper limit values of the plurality of operation amounts. In addition, a ratio between amplitudes having close conditions of the upper limit values of the operation amounts is calculated. Then, the heater is determined to be out of the rated range for an upper limit value of the operation amount or more at a time when the ratio is smaller than a threshold and sets the upper limit value of the operation amount at that time as an upper limit value of the operation amount at the time of executing a normal PID control operation. Meanwhile, Patent Literature 2 discloses a technology for setting an upper limit value of the heating value of a heater on the basis of the air temperature inside a casing of a thermostatic bath.